Predicting bed expansion and phase holdups for three-phase fluidized-bed reactors with and without biofilm

A predictive model is developed for the hydraulic behavior, such as bad height and overall gas, liquid, and solid holdups (volume fractions), of three-phase fluidized-bed reactors. The model uses process parameters, such as reactor dimensions, particle properties, and gas and liquid flowrates, as input variables. A wake model is applied to predict the liquid holdup, while the solids holdup is obtained by iteration based on material balance. Experimental results to evaluate the three-phase fluidization model are obtained from a laboratory-scale reactor using two sizes of clean glass beads under wide range of gas and liquid velocities. Modeling predictions and experimental results agree quantitatively for two-phase and three-phase conditions. The model is further applied to analyze fluidized beds with biofilm-coated media. Biofilm accumulation alters the drag coefficient (C_D) and bed expansion index (n). Applying a modified correlation for C_D to biofilm systems found in literature, the authors propose a new correlation for n which shows little dependence on the particle terminal Reynolds number.